Fermi resonances adiabatic exchange approximation

In this section we shall give the connections between the nonadiabatic and damped treatments of Fermi resonances [53,73] within the strong anharmonic coupling framework and the former theory of Witkowski and Wojcik [74] which is adiabatic and undamped, involving implicitly the exchange approximation (approximation later defined in Section IV.C). 

Figure 7. The Fermi resonance mechanism within the adiabatic and exchange approximations. F, fast mode S, slow mode B, bending mode.

Figure 12. Hydrogen bond involving a Fermi resonance damping parameters switching the intensities. The lineshapes were computed within the adiabatic and exchange approximations. Intensities balancing between two sub-bands are observed when modifying the damping parameters (a) with y0 =0.1, and y5 = 0.8 (b) with ya = ys = 0.8 (c) with yB — 0.8 and ys — 0.1. Common parameters oto = 1, A = 150cm, 2g)5 = 2850cm-1, and T = 30 K.

F. Fermi Resonance Within Adiabatic and Exchange Approximations... 

SD With Fermi Resonance, Beyond Adiabatic, Harmonic and Exchange Approximations [59]... 

In conclusion, note that the quality of the theoretical SD with respect to the experimental line shape is not as good for crystalline adipic acid as for the gaseous and liquid carboxylic acids studied above. The reason is that if Fermi resonances seem to be unavoidable in order to reproduce all features of the experimental line shapes and to conserve a good stability of the basic physical parameters when changing the temperature, however, the way in which the Fermi resonances are taken into account is very sentitive to the used adiabatic and exchange approximations [82]. 

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